1. Field of the Invention
The present invention relates to velocity calculating apparatuses, and more particularly, to a velocity calculating apparatus for calculating a velocity from a signal output from an acceleration sensor, for use in a navigation system for a motor vehicle.
2. Description of the Related Art
In a conventional navigation system for a motor vehicle, the positional information of the motor vehicle is obtained from a GPS signal.
Therefore, at places where a GPS signal cannot be received, such as a tunnel, a location behind a building, and a location under an elevated railroad, the positional information of the motor vehicle cannot be obtained.
To obtain the positional information of a motor vehicle even at a place where a GPS signal cannot be received, a velocity calculating apparatus has been developed in which a signal output from an acceleration sensor detecting the acceleration of a motor vehicle is integrated in the time domain to calculate the velocity of the motor vehicle. With the use of such a velocity calculating apparatus, the velocity of a motor vehicle can be calculated even at a place where a GPS signal cannot be received, and the mileage of the motor vehicle can be obtained by integrating the calculated velocity in the time domain. Therefore, a distance traveled by a motor vehicle after a GPS signal can no longer be received, and thereby, the positional information of the motor vehicle, can be obtained with the use of the velocity calculating apparatus.
However, the velocity calculating apparatus may have a large error caused by temperature drift and the sensitivity-temperature characteristic of the acceleration sensor, and by the acceleration of gravity at a slope when a signal output from the acceleration sensor is integrated to calculate the velocity.